Amplification of audio signals can be carried out using various methods, including analog, digital, and vacuum tube circuitry. While each method has distinct advantages/disadvantages, amplification of electric guitar signals is most often carried out using vacuum tube-based amplifier circuits. Part of the reason for the continued popularity of tube amplifiers for this application involves the way in which a tube amplifier responds when overloaded. When a tube amplifier is overloaded, the signal is clipped in a distinct way (relative to other amplification methods), often referred to as “soft.” _ENREF_2 Overloading a solid state amplifier produces “harsh” and “buzzy” sounds, which are often subjectively evaluated as inferior. As a result, beginning in the late 1970s (shortly after the introduction and largely the failure of the first solid state amplifiers) a variety of analogue devices that were specifically designed to emulate tube-type clipping appeared on the market. These devices used circuitry designed with gain compression (soft clipping) as a primary goal. Subsequently, this market exploded in the last several decades to include a large number of distortion circuits.
One of the most popular ways to simulate soft clipping involves placing parallel diodes with opposite polarity in the feedback loop of an operational amplifier. Various configurations have been employed based on the take-off voltages, the degree of conduction onset of the diodes, and other factors. The many different configurations offer distinct sounds, and these are subjectively preferred by different users. Thus, there is significant demand for new components which can tailor the type of clipping and produce different types of distortion and “sounds.”
Several examples of soft clipping circuits have been discussed in the patent literature _ENREF_6. All prior examples discuss general circuits using conventional components. We have not found prior art on incorporation of a molecular junction into a circuit in order to exploit the non-linear aspects of its electronic characteristics.
The molecular junction structure and its nonlinear response is the subject of previous patents assigned to Ohio State University, namely U.S. Pat. No. 7,112,366 and U.S. Pat. No. 7,042,006. To the authors' knowledge, no previous patents, presentations or publications disclose the use of molecular or tunneling junctions in audio distortion, processing, or amplification circuits.